[vaprdev]

Summary

Daytime scenes looked flat: the far hills were as saturated as the foreground and the ground was one even tone. A new src/grade.ts adds depth once in layout(), and every wallpaper's day palette is retuned.

 layout()
   paintSky()
+  sky = hdr.slice()
   paint far layer
+  haze(hdr, sky, ...)     fade toward the sky behind it, more with distance
   paint near layer
+  mottle(hdr, ...)        broad warm/cool ground patches in perspective
 Canvas
+  frame = 0..1            darken the bottom corners to frame a bright foreground

Also softens tundra drift ripples by day and keeps the ocean's ridges from brightening. haze and mottle are exported from the API and documented in CONTRIBUTING.

Evidence

Before (main) on the left, after on the right.

Behind text, as the terminal shows it

Verification: bun run typecheck passes; CI's check job runs dev/check.ts on this branch.

Merge Danger

Door: two-way

Blast Radius: visuals

Day looks of all ten wallpapers; two new API exports.

Merged together with the other visual improvements in #1; this PR's CI screenshot check fails by design because screenshots are regenerated there.